1. Field of the Invention
The invention relates to statistical block copolymers having improved properties, process for their manufacture and their use.
2. Discussion of the Background
Numerous statistical copolymers based on conjugated dienes and styrene are known which serve for the manufacture of tire treads. More specifically, reference is made to
1. Statistical butadiene-isoprene-styrene copolymers,
2. Block copolymers based on dienes and a vinyl aromatic compound, and
3. AB-block copolymers based on butadiene, isoprene and styrene. Regarding 1:
From DE-OS 33 10 118 vulcanizable compositions are known which comprise as an essential component polyisoprene and/or amorphous isoprene-styrene copolymers. The polymers are manufactured at different starting and end temperatures.
German patent application P 37 24 870.7 relates to a process for the manufacture of copolymers based on butadiene, isoprene and styrene in which an ethylene glycol ether of the formula R.sub.1 -O- CH.sub.2 - CH.sub.2 -O- R.sub.2 is employed as a cocatalyst. R.sub.1 and R.sub.2 are alkyl groups having variable numbers of carbon atoms from the groups methyl, ethyl, propyl and butyl. According to that process, copolymers are available in which more than 70% of the isoprene units are present in the 1,2-and 3,4-positions and more than 60% of the butadiene units are in the 1,2-position.